Device and method for side-impact identification

ABSTRACT

A device and a method, respectively, are proposed to detect side collisions, in which a temperature sensor is located in a motor-vehicle side section. In case of a side collision, the temperature sensor measures the short-term adiabatic temperature increase and a control device detects a side collision as a function of the measured temperature increase and the temperature gradient. A triggering decision is made by plausibility testing using an acceleration sensor.

BACKGROUND INFORMATION

The present invention is based on a device and a method for detecting side collisions according to the species defined in the independent claims.

A device for detecting side collisions is known from the European Patent EP-667 822, in which a pressure sensor is located in a side section of a vehicle body. When a side collision occurs, the adiabatic pressure increase in the side section is evaluated for side-collision detection. The side section is substantially closed in this case. Adiabatic means that the amount of heat remains constant.

SUMMARY OF THE INVENTION

The device and the method according to the present invention for detecting side collisions having the features of the independent claims have the advantage over the related art that a temperature sensor located in the side section of the vehicle body is less complicated than a pressure sensor. This results in cost savings. Also, no filtering of noise signals, such as acoustic frequencies, is required. Furthermore, the device according to the present invention and the method of the present invention are robust and react to actual deformations of the vehicle body. Thus, the method and the device according to the present invention are less sensitive with respect to events (driving through potholes, driving over the curb or slamming of the door) that suggest a side collision, but are not supposed to trigger a restraint system.

By the measures and further refinements mentioned in the dependent claims advantageous improvements of the device and the method for side-collision detection according to the present invention are made possible.

It is particularly advantageous that the temperature sensor is designed as a micromechanical sensor, so that the temperature sensor is easy to manufacture in mass production. The micromechanical sensor could be an extremely precise temperature sensor.

By designing a housing around the temperature sensor in the side section of the vehicle it is protected against radiation, and the adiabatic effect is increased since the air surrounding the temperature sensor is better insulated.

Using an acceleration sensor also has the advantage that a plausibility signal is generated, which is used to check a triggering signal obtained as a result of the temperature-sensor measurement. In this way, undesired triggering decisions for a restraining device and unnecessary injuries are prevented and costs are saved for the user of a restraint system. As an alternative, it is also possible that the acceleration sensor makes the triggering decision, and the temperature sensor generates the plausibility signal.

Furthermore, it is advantageous that the restraint devices are only triggered if the absolute temperature change and a temperature gradient exceed specified threshold values. It is ascertained especially with the temperature gradient that the temperature increase is short-term, so that a warming as a result of the vehicle being exposed to sunlight does not lead to an undesired triggering.

Finally, it is also advantageous, on the one hand, that redundancy is obtained by arranging a plurality of temperature sensors in a side section of a vehicle and, on the other hand, a temperature sensor will in each case be located near a deformation location of the side section.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the present invention are shown in the drawings and are explained in detail in the following description.

The Figures show:

FIG. 1 a side section with a temperature sensor;

FIG. 2 a block diagram of the device according to the present invention;

FIG. 3 a diagram comparing the temperature change with the relative volume change;

FIG. 4 a micromechanical temperature sensor in side view;

FIG. 5 a top view of the micromechanical temperature sensor;

FIG. 6 the micromechanical temperature sensor in a housing; and

FIG. 7 a flow chart of the method according to the present invention.

DESCRIPTION

Restraining systems, such as airbags, find increasing use in motor vehicles. Primarily, it is important in this context to rapidly detect an accident so that restraining means such as airbags and belt tighteners may be used efficiently. However, it is equally important to prevent an undesired triggering of restraining devices. Especially in a side collision the reaction time for the side-collision sensor system and the control system of the restraint systems is considerably shorter than in a head-on collision. A side collision in a side section of the passenger compartment should be detected early by the beginning deformation of the side section. Since side sections often constitute a substantially closed body, i.e., a cavity, an adiabatic pressure increase results in response to a deformation of the side section, which is accompanied by an adiabatic, rapid temperature increase. According to the present invention, at least one correspondingly fast temperature sensor is located in a side section of a vehicle, to detect side collisions. The collision force and/or the collision speed are ascertained by evaluating the absolute temperature increase and the temperature gradient, and the assurance is obtained that an adiabatic temperature increase is involved. The impact force and/or the impact speed may be determined based on the degree of deformation of the side section within a specified period of time. Combining the temperature sensor with an acceleration sensor allows a plausibility check of the temperature sensor's side-collision signal. Thus, it is ascertained whether an actual side collision is involved and not a temperature increase caused, for instance, by a welding torch.

The fast temperature sensor may be advantageously designed as a micromechanical temperature sensor. Micromechanics make a temperature sensor possible that is capable of very precise temperature measurements, and a micromechanical sensor is easy to produce in mass production.

FIG. 1 shows a side section 1 of a vehicle in which a temperature sensor 2 is located. Side section 1, here a vehicle door, has temperature sensor 2 in a cavity of the side door, depicted here as a functional block. Not shown is the evaluating electronic system, which may either be arranged in side door 1 together with temperature sensor 2 or may be arranged externally at some other location in the motor vehicle. A measurement amplifier, for instance, may be integrated on the chip with the temperature sensor, while digitization is carried out in a control device.

FIG. 2 shows a block diagram of the device according to the present invention. Temperature sensor 2 is connected to an input of a signal-processing unit 3. A data output of signal processing unit 3 leads to a vehicle bus 4 to which a control device 5 is connected. Control device 5 is connected to restraint means 6 via a data input/output. Component parts of the electronic system, i.e., the measurement-value amplifier and the analog-digital converter, may be arranged in alternative fashion as described above.

Temperature sensor 2 generates electrical signals corresponding to the temperature, which are amplified and digitized by signal-processing unit 3. These digital data are then transmitted via bus 4 to control device 5, which processes the digital data in such a way that the absolute temperature increase is compared to a specified threshold value and the temperature gradient is also compared. The temperature gradient indicates the temperature change per time. In this manner it is ascertainable whether an adiabatic air-pressure increase is involved or not. In an adiabatic process, the temperature increase must occur within a very brief period of time. If the absolute temperature increase and also the temperature gradient exceed specified threshold values, which were experimentally determined, a triggering signal will be generated that will be checked with a measuring signal of an acceleration sensor, if necessary. The measuring signal of the acceleration sensor indicates whether a side collision could indeed be involved or not. Thus, a plausibility check is carried out. If even this measuring signal is above a specified enabling threshold, the triggering decision is accepted and restraint means 6 are triggered. Airbags and belt tighteners are such restraint means 6.

FIG. 3 shows a diagram which relates the temperature change in a side section of a vehicle implemented as a cavity to the relative volume change. For instance, in case of a volume change of approx. 10%, a temperature increase of 13 Kelvin will already be obtained. This ensures that a side collision is already detected at an early deformation and a triggering decision may be generated. Since the door is not perfectly sealed, air escapes from the door during and after the side collision, so that soon after deformation the pressure and temperature will have reached approximately the values that prevailed before the side collision. This means that a lower degree of sealing of the door will result in decreased sensitivity of the side-collision detection according to the present invention. A relationship exists between the air temperature prior to the event, temperature To, the temperature increase ΔT and the volume change ΔV. In the leading area for small times (in the milli-second range), the pressure loss after the side collision due to door permeability is negligent, and the following result will be achieved for the adiabatic state change with the aid of measured temperature T₀+, ${\Delta \quad T\text{:}\Delta \quad T} = {{T_{0}\left( {\left( \frac{V_{0} - {\Delta \quad V}}{V_{0}} \right)^{1 - K} - 1} \right)}\quad {with}\quad K\quad {being}\quad {the}\quad {adiabatic}}$

exponent of the air and V₀ the door volume. From this, temperature change ΔT may be estimated, an ambient temperature of T₀=293 Kelvin and a decrease in the door volume of 10% resulting in a temperature increase of approximately 13 Kelvin.

FIG. 4 shows a side view of a micromechanical temperature sensor, which is arranged in a side section of the motor vehicle according to the present invention. A temperature sensor 7 made of platinum is implemented on a membrane 8 having poor thermal conductivity. Membrane 8, in turn, is arranged on a silicon frame 9 produced by means of microstructuring. Membrane 8, in this case, is made either of silicon dioxide or of silicon nitride, which are known dielectrics in semiconductor technology. These dielectrics have poor electric conductivity and thus also poor thermal conductivity. As an alternative, other dielectrics may be used.

Temperature sensor 7 is implemented as a platinum thin-layer element and has a temperature-dependent resistor. Thus, the temperature on membrane 8 may be inferred by measuring the resistance of the platinum element. Since the thermal capacity of membrane 8 is very low due to minimal thickness and low mass, membrane 8 very quickly assumes the temperature of the ambient air. Due to its low thermal conductivity, membrane 8 is thermally decoupled from the silicon frame and the body shell connected thereto, so that a temperature increase of the platinum element may occur without the thermally inert body shell, which has a large mass with a large heat capacity, having to be heated also.

FIG. 5 shows a top view of the micromechanical temperature sensor. Membrane 8 is located on silicon frame 9. Platinum sensor 7 has conductors 10 (printed circuit traces) leading to so-called bond pads to which the terminal wires, which provide the connection to other electrical or electronic components, must be soldered or bonded.

In FIG. 6, micromechanical temperature 13 shown in FIGS. 4 and 5 is accommodated in a housing. The housing includes a housing base 15 to which temperature sensor 13 is attached, and a housing top 12 having an opening 14 through which a pressure change in the ambient air is transmitted. If an adiabatic process is involved, this pressure change is accompanied by a temperature change.

In FIG. 7, the method according to the present invention is represented as a flow chart. In method step 16, a temperature signal from temperature sensor 2 is amplified by signal processor 3 and digitized and transmitted to control device 5. In method step 17, control device 5 calculates the absolute temperature increase and the temperature gradient. In method step 18, the absolute temperature increase and the temperature gradient are compared to predefined threshold values to ascertain whether a side collision has occurred or not. If both threshold values are exceeded, a side collision is present, and this detected side collision is checked in method step 19 using signals from an acceleration sensor. If the signal from an acceleration sensor is also above an enabling threshold, i.e., the acceleration in the lateral direction of a vehicle, it will then be determined in method step 20 that it exceeds an enabling threshold, and a triggering decision will be transmitted to restraint means 6 in method step 21.

If it was determined in method step 18 that either the absolute temperature increase or the temperature gradient is below the individually specified threshold value, a return to method step 16 is implemented, and the instantaneous temperature value is checked. If it was detected in method step 20 that the signal of the acceleration sensor is below the specified enabling threshold, a return to method step 16 is also implemented to call up the ambient-temperature signal.

Rapid information regarding the thus occurring temperature increase ΔT may also be obtained by a slower temperature sensor, by measuring the temperature gradient. In the first 20 ms after deformation begins, the temperature increase occurs according to an exponential function:

T(t)=ΔT(1−e ^(−t/τ))

τ is the thermal time constant of the air-temperature change in the vehicle cavity. It is experimentally determined and is assumed to be constant over the temperature and service life.

If this temperature is measured, for instance, after 0.5 ms and after 2 ms, the following is obtained:

T(0.5 ms)=ΔT(1−e^(−0.5 ms/τ)), and

T(2 ms)=ΔT(1−e^(−2 ms/τ)), respectively, and thus

ΔT=(T(2 ms)−T(0.5 ms)):(e^(−0.5 ms/τ)−e^(−2 ms/τ))

The relatively slow temperature sensor assumes temperature increase ΔT, for example, only after 50 ms, that is, much too late. Nevertheless, with the aid of this “trick”, information regarding the occurring ΔT is obtained already after 2 ms and then compared to a specified threshold value to detect a side collision.

An alternative method is to evaluate the first derivative of the temperature variation. The actual temperature increase must be seen as a jump function, which is made of a thermal substitute circuit diagram of the temperature sensor, made of a thermal resistor r and a thermal capacitance. The temperature is tapped off by way of the thermal capacitance. A differential equation results from the analog voltage cycle and the current equation, the differential equation simulating the jump function by a sum of the weighted first time derivative of the temperature variation and the temperature variation per se. The weighting results from the values for the thermal resistance and the thermal capacitance, which depend on the technological properties of the temperature sensor. Using a slow sensor, information regarding the temperature rise may already be available after a few ms. In a further refinement it is provided that only the first time derivative of the temperature variation is used to predict the temperature rise. 

What is claimed is:
 1. A system for detecting a collision on a side section of a vehicle body, comprising: a control device; and at least one temperature sensor located in the side section of the vehicle body and electrically connected to the control device, wherein the control device uses electrical temperature signals of the at least one temperature sensor to detect a temperature change indicating a side collision.
 2. The system of claim 1, wherein the at least one temperature sensor is a micromechanical sensor.
 3. The system of claim 1, wherein the at least one temperature sensor is accommodated in a housing in the side section of the vehicle body.
 4. The system of claim 1, further comprising at least one acceleration sensor electrically connected to the control device.
 5. The system of claim 4, wherein the vehicle has a restraint system, and wherein the control device makes a second comparison of an enabling threshold value with a signal of the at least one acceleration sensor, and wherein the control device triggers the restraint system if the signal of the at least one acceleration sensor exceeds the enabling threshold.
 6. The system of claim 1, wherein the vehicle has a restraint system, and wherein the control device determines from the temperature signals of the at least one temperature sensor at least one of a temperature change and a time derivative of the temperature change, and wherein the control device makes a comparison of at least one threshold value to at least one of the temperature change and the time derivative of the temperature change, and wherein the control device triggers the restraint system based on the comparison.
 7. A method for detecting a collision on a side section of a vehicle, the vehicle having a restraint system, the method comprising: generating temperature signals from a sensor located in the side section of the vehicle; and using the temperature signals to detect a temperature change in the side section of the vehicle, whereby a side collision is detected based on the change in the temperature.
 8. The method of claim 7, further comprising: determining, from the temperature change, a time derivative of the temperature change; comparing at least one threshold value to at least one of the temperature change and the time derivative of the temperature; and making a control decision to trigger the restraint system based on the comparison.
 9. The method of claim 8, further comprising: using an acceleration sensor to generate an acceleration signal; comparing an enabling threshold value to the acceleration signal; and triggering the restraint system if the acceleration signal is greater than the enabling threshold value. 